Polymeric ball valves are widely used for a variety of industrial applications. Polymeric ball valves typically provide the advantages of relatively light weight, low cost, corrosion resistance, and the ability to be welded on site into a piping system.
A known method of forming a polymeric ball valve includes providing a polymeric body/end piece and a polymeric end piece. A valve ball is disposed in the body/end piece and the end piece is fused to the body/end piece to enclose the valve ball in an integral valve body. A pair of resilient, ring-shaped seats provide seals between the ball and the body/end piece and the end piece. Each seat is held in place by a respective ring-shaped seat retainer. An example of a valve of this construction is disclosed in U.S. Pat. No. 5,232,201 to Spears et al.
A preferred method for forming a ball valve of the type described includes inserting a first seat, a first seat retainer and the ball into the body/end piece. Thereafter, a second seat retainer, a second seat and the end piece are placed over the ball and the end piece is fused to the body/end piece.
During the assembly procedure, the seats should be maintained in the desired position to ensure proper mating between the seats and the ball. One method for holding the seat retainer, and thereby the seat, in place includes providing flanges projecting inwardly from the body/end piece and the end piece, outer threads on the flanges and inner threads on the seat retainers. The seat retainers are screwed onto the flanges and thereby held in place. However, the threads must be molded, machined or otherwise formed on the body/end and end pieces. The thread formation may add significantly to the cost and inconvenience of manufacturing the valve. In particular, because the seat retainers and the body/end and end pieces are typically formed of polyethylene or polypropylene, care must be taken in forming the threads. Furthermore, care must be taken in screwing the seat retainers on to avoid cross-threading and damaging the threads. Additionally, a tendency may exist to distort the seat as the seat retainer rotates into engagement with the seat, or to apply too much or too little pressure to the seat by under-tightening or over-tightening the seat retainer.
Polymeric ball valves (and other valves including rotatable valve members) may be provided with a gearbox to facilitate rotation of the ball to open and close the valve. Typically, the gearbox includes a casing, a gear reducer and a drive shaft adapted to engage a valve stem which is connected to the ball. Drive means such as an electric motor may be disposed in or on the casing or otherwise associated with the gearbox.
In order to secure the gearbox to a polymeric ball valve, it is known to provide an integral upstanding flange on the valve body. The flange surrounds the valve stem. Holes are formed radially through the flange. The gearbox may be mounted on the flange by inserting bolts through the holes.
The foregoing gearbox mounting arrangement may suffer from a number of potential drawbacks. The provision of an upstanding flange which is strong enough and secure enough to resist torque from the gearbox without failure may add significantly to the weight and to the cost of forming the valve. Moreover, it may be necessary to provide a special bracket on the gearbox to allow mounting on the flange.